In general, a pigment having a small particle diameter exhibits strong cohesive force between pigment particles and thus is often insufficiently dispersed in media, such as organic solvents and melted polymers. Insufficient dispersibility of a pigment affects the tint strength of the pigment.
Thus it has been proposed to use a pigment in combination with a dispersant for dispersing the pigment to improve the dispersibility of the pigment. In particular, researchers have been focusing on improving the dispersibility of a pigment in toner particles, proposing various dispersants for use in toners of different colors including yellow, magenta, cyan, and black.
More specifically, PTL 1 discloses the use of a compound having an azo skeleton as a dispersant to improve the dispersibility of an azo pigment in yellow toner.
PTL 2 discloses the use of a particular polyester-based dispersant to improve the dispersibility of a magenta pigment in magenta toner.
PTL 3 discloses that a polymer containing sodium styrene sulfonate as a monomer unit is used as a dispersant to improve the dispersibility of a phthalocyanine pigment in cyan toner.
PTL 4 discloses the use of a copolymer composed of a styrene-based monomer and an acrylate-based (or methacrylate-based) monomer as a dispersant to improve the dispersibility of carbon black in black toner.